There is a significant need for a liquid pavement marking composition that will provide increased durability and retained reflectivity once applied to a surface and dried or cured. Compositions of this type are typically used on roads, highways, parking lots, and recreational trails, to form stripes, bars and markings for the delineation of lanes, crosswalks, parking spaces, symbols, legends, and the like. They are typically applied by spray coating (i.e., painting) the pavement surface. Preformed pavement marking sheets or tapes have also been used to mark pavement or traffic bearing surfaces.
Pavement marking stripes, or pavement markings of other shapes, may include reflective optical elements adhered to the pavement surface by the use of a binder. Current traffic paint systems typically use conventional 1.5 n.sub.D glass microspheres for retroreflection. The microspheres are typically flood coated onto the wet marking immediately after coating. This provides the paint with improved retroreflectivity and also covers the top surface of the uncured or undried coating with a protective layer of microspheres. This protective layer allows the markings to be exposed to traffic sooner because of the layer of microspheres over the surface, which prevents transfer of the coating to the surface of vehicle tires. This is important for rates of marking application. The time between application and the point where material will no longer transfer to vehicle tires is defined as the "track-free" time. Shorter track-free times increase marking efficiency by reducing or eliminating the need for traffic disruption through such measures as closing lanes or placing traffic control devices to protect such markings.
It would be advantageous to apply markings in a wider range of weather conditions than is possible with existing compositions. There is also a need for marking compositions with improved cure profiles to ensure both substrate wet out and rapid track-free time. Furthermore, improvements are needed to obtain compositions that are substantially free of volatile organic components.